Supply and Extract
Unit 3-Way Mix


Air handling units incorporating 3 way mix or air-mixing plenum are important elements in saving energy in Distribution Centres, Warehousing, Pharmaceutical and Data Centres or where the Air Handling Unit intended use is in a building or part of a building not designed for human occupancy as clarified under Ecodesign Commission Regulation (EU) No 1253/2014.

If the product is not designed for replacing utilised air with outdoor air, it is not a ventilation unit, unless the same product is also designed to replace only utilised air, and thus it should comply with all relevant requirements of the ecodesign measure.

In case the product has a connection to the outdoor with a supply / exhaust air flowrate in regular operation of minimum 10% of the total declared recirculated air flowrate, the unit is considered a ventilation unit and falls under Regulation 1253/2014.

Although not explicitly stated in the directive, a mixing box does not constitute heat recovery.


This investment passes off in several ways:

  • Lower energy consumption
  • Lower investment for heat generation and distribution
  • Less damage to the environment


The AHU air-mixing plenum combines two air streams and it is common for the supply and extract air handlers to be joined together, either in a side-by-side or a stacked configuration. The configuration includes three sets of dampers: one for the fresh air, one for the exhaust air, and a mixing damper between the two air streams. The mix of fresh air and recirculated air can thus be adjusted to suit the needs of the building. Typically as the fresh air and exhaust air dampers are driven from 0% open to 10% open, the mixing damper will in turn be driven from 100% open to 90% open, so as to always ensure a constant volume of supply and extract air.

Ancillary Items

Air filtration is always present in order to provide clean dust-free air to the building.

Direct heating, placed directly in the air stream, are direct heat exchangers and include those for gas-fired fuel-burning heaters or electric air heater batteries (EAHB).

Indirect Heating and Cooling coils use hot water or steam for heating, and chilled water for cooling. Heat pumps can be used as well. (Prime energy for heating and cooling is provided by central plant).

Humidification is often necessary in colder climates where continuous heating will make the air drier, resulting in uncomfortable air quality and increased static electricity. Various types of humidification may be used as part of our air handler and include evaporative, vaporizer, spray mist and wetted medium.

If dehumidification is required, then the cooling coil is employed to over-cool so that the dew point is reached and condensation occurs. A heater coil placed after the cooling coil re-heats the air to the desired supply temperature and humidity level. This is often used for chilled beam applications.

Intelligent Energy Controls

ECE Intelligent Energy Controls comes as a standard and monitors the return air quality, energy available to recover and CO2 concentration for optimum energy efficiency whilst maintaining desired fresh air requirements. Additionally, when outside air conditions are such, typically mid-season weather conditions, it may be that ambient temperatures are suitable for free cooling purposes. Where fresh air is not required, such as early morning pre heat or pre conditioning periods, the dampers can be automatically set to full re-circulation, again for optimum energy efficiency.



Buy Online